As is known rear lights of cars usually consist of a substantially basin-shaped, rigid rear body, which is structured so as to be stably recessed in a compartment specifically realized in the rear part of the vehicle body; of a front lenticular half-shell, which is at least partially made of transparent or semitransparent plastic material, usually possibly colored, and is arranged to close the mouth of the body so as to surface on the outside of the vehicle body; of one or more cup-shaped bodies with an approximately parabolic profile, each of which has a mirror-finished inner surface and is positioned within the rear body with its mouth facing a corresponding transparent or semitransparent portion of the front lenticular half-shell; and of a series of incandescent lamps, each of which is arranged close to the bottom of a respective cup-shaped body so as to backlight the portion of the front lenticular half-shell directly above the cup-shaped reflector body itself.
Furthermore, in some models of rear automobile lights, the front lenticular half-shell is provided with a narrow, elongated, i.e. ribbon-like, transparent or semitransparent portion, which usually surrounds at least one of the transparent or semitransparent portions of the front lenticular half-shell which are aligned with the mouths of the reflector cup-shaped bodies.
In order to uniformly backlight this ribbon-like portion of the front lenticular half-shell, some rear automotive light manufacturers have arranged a bar made of photoconductive material with an approximately circular section within the rear body, which bar seamlessly extends immediately underneath the inner surface of the front lenticular half-shell over the whole length of the same ribbon-like portion of the front lenticular half-shell; and a set of light emitting diodes, traditionally referred to as LEDs, which are positioned at both ends of the bar so as to direct the produced light directly into the body of the bar. The light then propagates into the photoconductive-material bar as a result of the same physical principles which govern the propagation of light within optical fiber cables.
Finally, the lateral side of the photoconductive-material bar which is opposite to the front lenticular half-shell is structured so as to direct some of the light which is propagated within the body of the bar towards the front lenticular half-shell so as to more or less uniformly backlight the entire ribbon-like portion of the front lenticular half-shell.
More in detail, the aforesaid lateral side of the photoconductive-material bar is provided with a flat longitudinal band which is locally substantially parallel to the surface of the front lenticular half-shell immediately above it, and with a multitude of rectilinear, triangular-section deflector prisms, which are appropriately distributed along said flat longitudinal band. These deflector prisms are additionally oriented perpendicularly to the centre line of the flat longitudinal band, and are arranged in sequence along the whole length of the flat longitudinal band of the bar, at a predetermined distance from one another.
While ensuring a significant cost saving as compared to a massive use of LEDs, the performance of the backlighting system by means of light-guide bars is not excellent when the photoconductive-material bar needs to be branched to take the light to two different sections of a same ribbon-like portion to be backlighted. Experimental tests have indeed indicated that the light extraction from the photoconductive-material bar body at the branches of the light-guide bar is not as uniform as in the rest of the bar body, and this very often produces/causes a locally irregular intensity distribution of the light crossing the ribbon-like portion of the front lenticular half-shell.
Regretfully, external observers perceives these “shadows” along the ribbon-like portion of the front lenticular half-shell as a fault of the rear light, and for this reason the major rear automotive light manufacturers have been forced to position LEDs at the distal end of each branch of the light-guide bar. Thereby, the light which is propagated within each branch of the guide-light bar comes from the LED(s) positioned at the distal end of the same branch and not from the branching from which the light-guide bar branch originates. This means that the light must not propagate within the light-guide bar branching in order to propagate within the light-guide branch.
In other words, each light-guide bar branch works in a substantially independent manner from one another. Obviously, this implies the use of a high number of LEDs, with resulting increase of costs.